Tension-compression testing machine



July 1 1965 J. M. KRAFFT ETAL 3,194,062

TENSION-COMPRESSION TESTING MACHINE Filed Oct. 25, 1962 2 Sheets-Sheet1.

TIME

INVENTOR5 JOSEPH M. KRAFFT JOHN C. HAHN MWTTORNEY y 13, 1965 J. M.KRAFFT ETAL 3,194,062

TENSION-COMPRESSION TESTING MACHINE Filed Oct. 25. 1962 2 Sheets-Sheet zINVENTOR5 PH M. KRAFFT United States Patent TENSIGN-CQMPRESSEGN TESTKNGMAHENE Joseph M. Kratft, Alexandria, Va, and .l'ohn tC. Hahn,Washington, D.C., assignors to the United States of America asrepresented by the Secretary of the Navy Filed Oct. 25, 1962, Ser. No.233,166 4 Uaims. (Cl. 7393) (Granted under Title 35, US. Code (1952),see. 266) The invention described herein may be manufactured and used byor for the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

The present invention is directed to materials testing machines and moreparticularly to a machine for applying either tensile or compressiveloads through a single head movable at high speeds. In many materials,important strain rate effects can be observed by increasing head speedabove that possible in conventional testing machines. These can beinvestigated with machines capable of high head speed coupled withinstrumentation for measuring load and displacement at such speeds. Mosttestingmachines capable of high loading rates ancl/ or of high headspeed can be classified in one of two groups: those loading (1) by rapidexpansion of a pressurized gas, or (2) by impact of a massive hammer.Generally, gas loaders are preferred to cover the speed rangeapproaching that possible with standard machines as an impact hammerwith suflicient momentum at low speeds would be too massive. However,the simplest gas loaders, because of the gas compressibility, areinherently soft; their stiffness can be increased by requiring thepressurized gas to displace a hydraulic fluid through a restrictivepassage in addition to requiring it to load and deform the specimen. Thepresent invention is a hydraulically stiffened type gas actuated rapidloader.

It is therefore an object of the present invention to provide a testingmachine capable of high speed, and a uniform rate of loading for tensileor compressive testing of notched or unnotched specimens.

Another object is to provide a single, quick opening valve which servesdual functions of initiating head motion and of throttling thestiffening liquid in order to restrict head speed.

Another object is to provide a testing machine which may be adjustablefor different speeds.

Still another object is to provide a testing machine which can beoperable from a remote location.

Yet another object is to provide a test machine which is easilyadaptable for either tensile or compression testing of materials withinthe same head space.

Other objects and advantages of the present invention will becomeapparent to those skilled in the art as the disclosure is made in thefollowing description of the invention illustrated in the accompanyingdrawings, in which:

FIG. 1 illustrates a cross sectional view in elevation; FIG. 2illustrates a schematic drawing of the testing machine, related pressurelines, and control valves;

FIG. 3 is a top view which illustrates a valve control handle forsetting the rate of loading control and a scale that represents theamount of rotation of the control which indicates the valve opening; and

FIG, 4 illustrates different scope traces representing loads vs. timefor different settings of the throttle valve control.

FIG. 5 illustrates an enlarged view of the drive holding means foradjusting the opening of the valve.

The head of the present testing machine is drawn by a piston which ispressurized on one side by an expandable gas and on the other side by arather incompressible liquid. Head displacement is controlled by ameter- 3,194,062 Patented July 13, 1965 ing valve which opens to permitthe How of hydraulic fluid, and thus the onset of head movement. Themetering valve may be preset to open to any certain degree so that theresulting degree of throttling effects control of the speed of travel ofthe piston. The testing machine is provided with additional valves andcontrols which are operated to control the direction of movement of thepiston and the amount of pressure available to drive it.

Now referring to the drawings there is shown by illustration atensile-compression testing device. The device comprises a housing 19made of two sections 11 and 12 with section 12 having an end portion 13that telescopes into section 11 with the upper portion extending outover section 11 with their outer wall surfaces in alignment. The endportion 13 has a cutout 14 along the circumference of the outer surfacethereof within which a suitable gasket or O-ring 15 is placed to preventfluid leakage between the inner wall surface of section 11 and the outerwall surface of end portion 13 of section 12. The end portion 13 thattelescopes into section 11 has a concave lower surface 16 and the uppersurface of section 12 is also concaved to form surface 17. An apertureis centrally located in section 12 between the lower and upper concavedsurfaces 16 and 17 to form wall surface 18. The diameter of the apertureadjacent to surface 16 is less than the diameter of the remainder of theaperture to form a shoulder 21 near the end surface 16. The wall surfaceformed by the aperture is provided with threads 22 which extend for ashort distance starting at the upper end surface 17. Between thethreaded portion 22 and the shoulder 21, the wall surface 18 is providedwith circumferential rectangular cutouts 23 within which suitable seals24 are placed. Within the aperture between the end surfaces 16 and 17 isplaced a throttling valve 25 made in the shape of a double cone forregulating a flow of fluid in either direction through a matchingpassage formed respectively by upper and lower valve seats 26 and 27which contain the throttling valve 25. The lower valve seat 27 is formedwith an upper portion that ap- 'proximates the diameter of the apertureand a lower portion that closely fits against the aperture wall of leastdiameter. Thus the upper portion of valve seat 27 rests against shoulder21. The valve seat surface converges downwardly toward the center and isparallel with the lower portion of the double cone shaped throttlingvalve 25. The lower portion of the valve seat 27 is rounded away fromthe center and aligns with the concave end surface 16 of the end portion13 of housing section 12. The upper valve seat is similar to the lowervalve seat with the valve seat wall surface converging upwardly towardthe center, and parallel to the upper portion of throttling valve 25 acylindrical threaded nut screws down against the upper valve seatsection in order to secure the valve seats in place. The nut has arounded throat section which smoothly meets with the valve seat surfaceand the upper end at concave surface 17. Gaskets 24 in rectangularcutouts 23 provide a seal between the valve seat sections and the wallof the aperture to prevent any fluid leakage therebetween.

The upper housing section 12 is provided with a flat plate or cover 23of sufiicient thickness to withstand desired high pressures and whichissecured in place by bolts 31 that pass through section 12 and arescrew threade into section 11. i

A piston-containing pressure chamber 30' is centered on top of cover '28and formed by a cylindrical member 33 and a cover 34 secured thereto bysuitable bolts 35 which pass through the cylindrical member 33 and screwinto the cover 28. Suitable gaskets 36 are placed between thecylindrical member 33 and the cover 28 and between the cover 34 and thecylindrical member 33 to prevent any fluid leakage. The cover 34 is.much thicker at the center r about the axis than at the edge which issecured to the cylindrical member and has a portion 37 that extendsdownwardly into the chamber and a portion 38 which extends upwardly. Acylindrical cavity 41 is formed in the downwardly extending portion andextends upwardly a distance which is just beyond the level of the top ofthe thin portion of the cover. The cavity 41 meets with an aperture 42through the upwardly extending portion wherein the cavity is of greaterdiameter than the aperture 42.

The throttling valve is provided with an elongated valve stem 43 whichextends upwardly through the chamber 32 through the cover 28 and up intothe cavity 41 within the cover 34. A suitable gasket 44 is provided between the valve stem and the walls of the cover 28 through which thevalve stem extends. The fluid chamber 34 has therein a piston 45 whichis screw threaded onto the valve stem and held against rotation withinthe fluid chamber by a pin 46 secured in the downwardly extendingportion 37 of the cover plate and which extends into a cavity 47 in theupper surface of the piston. The upper end 4-3 of the valve stem ismachined to provide opposing flat surfaces such that the flat endportion slidably fits between a bifurcated end 49 of a coupling 51 whichpasses through the upwardly extending portion 38 of the top cover plate34-. The coupling is prevented from passing upwardly through theaperture 42 by a shoulder 52 within the cavity 41 and is held in placeby a collar 53 which is pinned onto a cylindrical portion 54 of thecoupling. A handle 55 is secured over the coupling by any suitable meanssuch as by pressure, as shown. The handle is adapted to rotate thecoupling which rotates the valve stem to adjust the clearance betweenthe valve 25 and either of the valve seats, 26, 27. Suitable markingsare applied near the rotating handle to indicate the adjustment of thevalve for a desired throttling opening.

A pressure chamber 60 is formed in the lower section of the housing 10between the lower surface 16 of the upper section and the inner surfacesof the lower section. A cylindrical weigh-bar 61 passes through anaperture 62 centrally located in the lower wall 63 of the lower section12 of the housing and connects with a piston 64 in the pressure chamberin the lower section of the housing. The piston 64 is formed at an anglewith the axis through the center of the housing in which the anglecorresponds to the angle of the concave surface 16 of the lower surfaceof the upper section of the housing. The weigh-bar 61 is screw threadedinto the piston stern and locked in place by a locking screw 65. Asuitable gasket is placed around each the piston and the weigh-bar toprevent passage of fluid between their surfaces and the surface of theiradjacent surfaces.

The housing is provided with a fluid passage 66 to admit a fluid into orvent a fluid from chamber 60 between the piston and the bottom wall ofthe lower section of the housing. A passage 68 in the upper section ofthe housing admits a fluid into or vents a fluid from the chamber 32between the cover 28 and surface 17 of the upper concave surface of theupper section of the housing. A passage '71 is made into the cover 28 toadmit a fluid into or vent a fluid from below the piston 45 withinchamber 36. A passage 72 is made through the cylindrical member 33 intochamber 34) to admit into or vent a fluid from the area above piston 45within chamber 30. A passage 73 is also made through the upper sectionof the housing to the area above piston 64 to admit a fluid underpressure into the area above piston 64 or to release the pressure abovepiston 64 through a passage 74 to the chamber 32 between cover 28 andthe surface 17 of the upper section of the housing. Each of the passagesthrough the housing is provided with a threaded portion 75 at theirinlet into the housing to provide a means by which suitable fluid can beforced into and vented from the respective areas above I and below thepistons.

The pistons and associated structure are for illustrative purposes onlyand are shown for the purpose of explaining the operation of the testmachine. A fluid under pressure, such as nitrogen, from a tank 7 6 isconnected through V a control valve 77 to a four-Way valve 78 which isconnected with the fluid passages 66 and 68 by suitable pressure linesfill and 82 to admit fluid under pressure to either pressure chamber 32or 60 depending on the operation desired. A second source of fluid underpressure from a separate tank Ma is directed through a control valve 77and a regulator valve 83 to a separate four-way control valve 78a. Fluidunder pressure is directed from the fourway control valve 78a to fluidpassages 71 and 72 through suitable pressure lines 81 and 82. Thefour-way control valves operate to permit passage through either of thevalves to either of the connected lines 81 or 82 and to vent the line 81or 82 not under pressure through vent 83 or in operation of the four-wayvalve, pressure is applied at the inlet 85 and it takes a path to outlet86 making line 81 the pressure line; when the valve is in this positionline 82 is vented through valve port 87 to the vent 33 with the passagebetween ports 87 and S5 closed. W'hen pressure is applied through line82 a path is open between ports 85 and 87 and between 86 and the vent 83with the path closed between 35 and 85. Thus the fourway valve allowsfluid under pressure to pass through one side of the valve to a pressureline while simultaneously opening a path through the valve to the vent.Each of the fluid lines to the four-way valves 7 8, 78a are adapted witha pressure gage 89 so that the pressure in each of the pressure linescan be determined for uniform operation.

The test machine is also provided with a hand or mechanical pump forpumping fluid from chamber 32 into chamber 69 above the piston 64 orfrom the chamber 6t above the piston 6-4- to the chamber 32. Amechanical pump 91 is connected with a three way control valve 92 whichin operation directs fluid to either chamber 32 or chamber 6i throughsuitable pressure lines 93 and 24- connected with passages 73 and 74depending on the position of the valve 92. Valve 92 has an off positionso that no fluid will pass through either path through the valve.

The bottom section of the housing has extending therefrom spaced,aligned, elongated, threaded columns 1M. A fixed crosshead res issecured to the bolts and'adjusted upwardly toward or downwardly awayfrom the housing to provide a member to which the specimen holders aresecured. The fixed crosshead is adjusted by a motor or any othersuitable means. In use of a motor, the motor is carried by the crossheadand drives drive gear wheels we and driven gear wheels which arethreaded onto the column 01. Specimen holder 1% is secured to thecrosshead and extends upwardly toward the housing and provides a meansto which a specimen is secured by specimen grips, not shown forsimplification of the drawings. For securing a specimen between theweighbar 61 and specimen holder M96 the fixed plate can be moved alongcolumns 161 to provide a spacing between the specimen holders to receivespecimens of different length.

The test machine is operative for either tensile or compression testing.In operation, the chamber 32 is supplied with hydraulic fluid andoperates as a reservoir for hydraulic fluid used in the operation of thetest machine. As such, the concave surface 17 insures that the hydraulicfluid will always flow downwardly toward throttling valve 25. Inoperation for tensile testing, the throttling valve 25 is set for thedesired flow of fluid through the valve passage. pressure container 76ais admitted to chamber 36 above piston 45 through valve 73a, line 82,and passage 72. Pressure above piston 45 forces the piston downwardlydisplacing any fluid out through passage 71, line 81, valve 78a, andvent 84. This forces throttling valve 25 open. With throttling valve 25open, fluid pressure from Fluid pressure from fluid pressure container76 is applied to chamber 32 above the hydraulic fluid therein throughvalve 78, line 82, and passage 68. Fluid pressure applied above thehydraulic fluid in chamber 32 forces the hydraulic fluid through thethrottling valve passage to the area above piston 64 and forces piston64 downwardly against stop 70 simultaneously forcing any fluid belowpiston 64 out through passage 66, line 81, valve port 86, and outthrough vent 83. With the piston 64 bottomed, the test material 95 isnow secured between weigh-bar 61 at one end and material holding element106 at the opposite end. i Valve 25 is now closed by pressurizingchamber 30 below piston 45 by a fluid under pressure from pressurechamber 76a through regulator valve 83, valve 78a, line 81 and housingpassage 71 into the chamber. The area above piston 45 is vented throughpassage '72, line 82, valve 78a, and vent 84. Valve 78 is now rotated toadmit a fluid pressure into chamber 60 below valve 64. Fluid pressure isadmitted from pressure container 76, through valve 78, line 81, andhousing passage simultaneously. Pressure is removed from chamber 32through housing passage 68, line 82, valve port 87, valve 78, and vent83. The test machine is now charged and ready for test. In load testing,the throttling valve is opened by setting valve 78a to apply pressureinto chamber 30 above piston 45 While venting the chamber below piston45 back through the valve. Pressure above piston 45 forces the pistondownwardly, opening throttling valve 25. When throttling valve 25 isopened, the hydraulic fluid under pressure above piston 64 is releasedand the fluid flows past valve 25 into chamber 32 in which the pressurewas previously released. Piston 64 rises as permitted by the dischargeof hydraulic fluid into chamber 32 around throttling valve 25, therebyapplying a tension on the test material. As long as a fluid pressurefrom fluid pressure container 76 is applied intochamber 60 below piston64, a tension will be applied to the test material. A pressure of 2000p.s.i. below piston 64 provides a maximum head speed of about 2 ft./sec.in the machine illustrated by the drawing and described in thespecification.

FIG. 4illustrates stress-strain load vs. time curves for differentclearance adjustments of the throttling valve. The record shown is fordifferent clearance adjustments as determined by different amounts ofrotation of the valve stem which sets the amount of the clearancebetween the throttling valve and the passage when in its full openposition as determined by the setting of the handle 55.

In operation for compression on the test material, throttling valve 25is adjusted to the desired clearance between the valve and the lowervalve seat 27. Valve 64 is then forced up to its maximum by pressure inchamber 60 applied under the valve. Pressure is applied above piston 45to close throttling valve 25 by forcing piston 45 downwardly. Highpressure is then applied to chamber 32 above the hydraulic fluid inchamber 32 simultaneously venting chamber 60 below piston 64. Themachine is now ready to apply a compression load on a test material heldin place between the holders. Valve 78a is rotated to apply a pressurein chamber 30 below piston 45 while venting the area above piston 45.This forces piston 45 upwardly, opening throttling valve 25. Openingthrottling valve 25 permits the flow of hydraulic fluid under pressurethrough the passage around the throttling valve into the chamber abovepiston 64. The pressure applied to piston 64 applies a compression forceon a test specimen. As long as pressure is applied from pressure chamber76 to the chamber 32, a compression force will be applied to the testmaterial.

Since the valves in the test machine are operated by fluid pressurecontrolled by separate valves, the valves, pressure chambers, etc., canbe remote from the test machine. This permits one, if desired, to placethe test machine in a hot cell where tension or compression can beapplied to materials that have been radiated by harmful radiation. Thusthe test machine of this invention permits material testing of materialsthat have been irradiated to determine the effects of any radiation onthe materials. By use of hand manipulators which are well known in theradiation field, the test material can be secured into the machine foroperation. The spacing of the passage open, ing about throttling valvecan be set by rotation of handle 55 by the hand manipulators or by amotor at tached thereto and which could be operated from outside the hotcell. Thus the test machine of this invention can be used to carry out afield ofresearch on materials which cannot be handled by hand because ofharmful effects of radiation.

For slow speed operation of the test machine, the throttling valve 25can be left open and the pressure can be controllably applied to eitherchamber 32 while venting chamber 60 or pressure may be applied tochamber 60 below piston 64 while venting chamber 32. Another possibilityis to pressurize both chamber 32 and the chamber 60 below piston 64 andthen controllably depressurize either of the chambers depending onwhether tensile or compresa sive testing is desired. The test machine isalso provided with a hand operated hydraulic pump 91 which can be usedfor fine adjustment of the load piston 64 and for applying tension orcompression testing. The hand pump 64 applies tension on the testspecimen. For compression testing, a gas pressure is applied belowpiston 64 forcing it into the up position. The specimen is connectedinto the specimen holders and hydraulic fluid is forced into the areaabove piston 64 applying a compression onto the test specimen.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that Within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A tensile-compression testing machine which comprises a housing, ahydraulic fluid reservoir in said housing, a piston chamber below saidreservoir, a centrally located passage between said reservoir and saidpiston chamber, a valve seat and a valve secured in said pas sage, fluidoperated control means connected with said valve to control passage ofhydraulic fluid through the passage between said valve and valve seat, apiston in said piston chamber, said piston chamber having a centrallylocated aperture through the bottom thereof, a weigh-bar piston rodslidably passing through the aperture in the bottom of said housing andsecured to said piston within said piston chamber, means for admittinga. gas into said reservoir above said hydraulic fluid and into saidpiston chamber below said piston and means for securing test specimenholding means below said housing.

2. A tensile-compression testing machine which comprises a housing, ahydraulic fluid reservoir in said housing, a piston chamber below saidreservoir and separated therefrom, a centrally located passage betweensaid reservoir and said piston chamber, a valve seat and matching valvesecured in said passage, fluid operated control means connected withsaid valve to control passage of hydraulic fluid through the passagebetween said valve and valve seat, a piston in said piston chamberadapted for movement along the linear axis of said housing, seal meansabout said piston to prevent fluid leakage between said piston and thepiston chamber wall, said piston chamher having an axially alignedaperture through the bottom thereof in said housing, a weigh-bar, pistonrod slidably positioned through said piston chamber aperture andconnected with said piston within said piston chamber, means foradmitting a gaseous fluid into said reservoir above said hydraulic fluidand into said piston chamber below said piston and for venting saidgaseous fluid from said reservoir and from said piston chamber belowsaid piston, and means positioned relative to said housing and weigh-barfor securing test specimen holding means.

3. A control means for controlling the rate of movement and direction ofmovement of an energy applying piston in a tensile-compression testingmachine which comprises a housing, a liquid fluid reservoir in saidhousing, a first fluid pressure chamber, an energy applying piston insaid first fluid pressure chamber, a partition separating said reservoirand said piston chamber, an axially aligned cylindrical passage withinsaid partition between said reservoir and said piston chamber, a pair oflinearly aligned valve seats secured in said cylindrical passage, anactivating and throttling valve positioned between said valve seats forclosing the passage by seating against either of said valve seats, asecond fluid pressure chamber, said second fluid pressure chamberpositioned above said reservoir and separated therefrom, a valve controlpiston in said second fluid pressure chamber, a piston rod threaded onone end and secured at said threaded end to said valve control pistonwith said screw threaded end extending into said second fluid pressurechamber above said valve control piston, a valve stern connected at oneend to said valve with the other end secured against rotation to saidpiston rod for axial movement therewith, means for admitting a fluidinto said second fluid pressure chamber on either side of said valvecontrol piston, means for venting fluid from either side of said valvecontrol piston, said valve control piston adapted to close said valveand to open said valve depending on the pressure applied to said valvecontrol piston, said valve controlling passage of fluid between saidvalve seats and said valve to control said energy applying piston, meansto supply a gaseous fluid under pressure into said reservoir and to ventgaseous fluid from said reservoir and means to supply a gaseous fluidunder pressure to said first pressure chamber below said energy applyingpiston therein and to vent gaseous fluid from said first pressurechamber from below said energy applying piston.

4. A tensile-compressive testing machine which comrises a cylindricalpressure vessel having cylindrical inner walls, a primary piston adaptedto slide along the inner wall of said pressure vessel, a connecting rodextending through said vessel and attached to said primary piston, areservoir in said pressure vessel above said primary piston, means foradmitting a hydraulic fluid to the side of said piston opposite fromsaid connecting rod, means for applying a gas under pressure to the sideof said piston connected to said connecting rod, said vessel providedwith a valve port between said reservoir and the primary piston, a valveseat in said port, a valve in said port for controllably releasinghydraulic fluid from above said piston to said reservoir, and from saidreservoir to said pressure vessel into the area above said primarypiston, a secondary cylinder secured to said pressure vessel above saidreservoir, a secondary piston in said secondary cylinder, means foradmitting a gas into and releasing a gas from said secondary vesselabove and below said secondary piston, means for connecting saidsecondary piston to said valve, adjustable means for adjustably limitingthe stroke of said secondary piston whereby operation of said secondarypiston operates said valve to limit a flow of hydraulic fluid throughsaid valve port to restrict the rate of movement of said primary pistondue to gas pressure thereon, and means for connecting a test specimenbetween said connecting rod and a specimen holder connected with saidpressure vessel.

References (Iited by the Examiner UNETED STATES PATENTS 2,371,450 3/45Langdon 91-4 X 2,834,569 5/58 Nickerson 251-62 2,854,919 10/58 VltavskylOO269 RICHARD C. QUEISSER, Primary Examiner.

JOSEPH P. STRIZAK, Examiner.

1. A TENSILE-COMPRESSION TESTING MACHINE WHICH COMPRISES A HOUSING, AHYDRAULIC FLUID RESERVOIR IN SAID HOUSING, A PISTON CHAMBER BELOW SAIDRESERVOIR, A CENTRALLY LOCATED PASSAGE BETWEEN SAID RESERVOIR AND SAIDPISTON CHAMBER, A VALVE SEAT AND A VALVE SECURED IN SAID PASSAGE, FLUIDOPERATED CONTROL MEANS CONNECTED WITH SAID VALVE TO CONTROL PASSAGE OFHYDRAULIC FLUID THROUGH THE PASSAGE BETWEEN SAID VALVE AND VALVE SEAT, APISTON IN SAID PISTON CHAMBER, SAID PISTON CHAMBER HAVING A CENTRALLYLOCATED APERTURE THROUGH THE BOTTOM THEREOF, A WEIGH-BAR PISTON RODSLIDABLY PASSING THROUGH THE APERTURE IN THE BOTTOM OF SAID HOUSING ANDSECURED TO SAID PISTON WITHIN SAID PISTON CHAMBER, MEANS FOR ADMITTING AGAS INTO SAID RESERVOIR ABOVE SAID HYDRAULIC FLUID AND INTO SAID PISTONCHAMBER BELOW SAID PISTON AND MEANS FOR SECURING TEST SPECIMEN HOLDINGMEANS BELOW SAID HOUSING.